Fiber-optic sensors are increasingly being used as devices for sensing some quantity, typically temperature or mechanical strain, but sometimes also displacements, vibrations, pressure, acceleration, rotations, or concentrations of chemical species. The general principle of such devices is that light from a laser is sent through an optical fiber and there the light experiences subtle changes and then reaches a detector arrangement which measures these changes.
In particular a growing application field is the use of fiber optic sensing system for acoustic sensing, especially Distributed Acoustic Sensing (DAS). DAS is quickly becoming recognized as a powerful tool for remote downhole sensing. The list of existing and potential applications for this new technology is long and continues to grow. Traditionally, DAS measurements are performed with single mode optical fiber (SMF), and not multimode optical fiber (MMF).
Distributed temperature sensing or DTS is a fairly mature and fairly widely deployed downhole oil and gas sensing technology that usually requires the use of MMF. For this reason, many hydrocarbon wells throughout the world already have MMF installed. The ability of using DAS with MMF can greatly expand the use of DAS in existing wells and will allow both types of measurements to be performed with one type of fiber.